This research proposal is designed to evaluate the transport relationhsips between the major anions of the glomerular filtrate, chloride, bicarbonate and phosphate, both under control circumstances and during experimental maneuvers of various kinds. In particular, it is planned to evaluate the presence or absence of a dysequilibrium pH in the proximal tubule, to study the rates of absolute chloride and bicarbonate, as well as phosphate transport when their delivery to the proximal nephron is increased in the absence of volume expansion and to investigate the possibility that bicarbonate may be reabsorbed as an ion as well as by the mediation of hydrogen ion secretion. Furthermore, those factors which are paramount in regulating proximal anionic transport will be identified, and the mechanism by which they influence electrolyte transport will be studied. The affect of these agents on the unidirectional flux rates (tubule-to-peritubular space and pertibular capillary-to-lumen) will be evaluated. By these avenues of approach, an attempt will be made to develop a single unifying hypothesis of anionic transport in the proximal tubule.